The present invention relates to improved adhesives for use with rugs and carpets. More particularly, the present invention relates to the use of low cost vinyl acetate-ethylene copolymer emulsions having a T.sub.g between about -35.degree. C. and about -10.degree. C. as laminating adhesives for rugs and carpets.
Adhesive compositions are essential to the structure of rugs and carpets. Tufted synthetic yarn could not function as a carpet without the presence of a latex adhesive to laminate a secondary fabric, such as jute or burlap, to the tufted primary fabric, which can also be jute or burlap. The latex adhesive functions to lock the tufts as well as bond the secondary fabric to the primary tufted material. Resins for this use are preferably applied in emulsion form to reduce costs and aid in controlling penetration into the textile fibers. To meet economic considerations such resins must be made as inexpensively as possible.
Basically, one of two types of backing construction is used by the industry today: (a) a secondary fabric is laminated by the use of latex adhesive to the primary fabric or (b) a foamed latex layer is applied directly over the fiber locking adhesive, which when dried and cured creates a sponge cushion as an integral part of the completed carpet. For either type of backing construction the resin employed as the latex adhesive must maintain its flexibility after application and not become either brittle or soft and tacky.
Double-backed tufted carpets are generally made by looping threads of pile fibers through an inexpensive woven or unwoven textile base, known as the primary substrate. The thread is looped through the primary substrate in one continuous length constituting a complete row of pile in the carpet. The thread is pulled tightly against the underside of the primary substrate, but the loops can remain connected or be severed, depending on whether a loop pile or a cut pile carpet is desired. The pile fibers are then anchored to the primary substrate in this arrangement by the application of adhesive. The double-backed tufted carpet is completed by applying to the wet underside of the primary substrate a further backing material known as the secondary fabric or as scrim. The scrim, which serves to improve the dimensional stability and appearance of the carpet, is normally adhered to the underside of the primary substrate by means of the same adhesive which serves to anchor the pile fibers to the primary substrate. The resulting laminate of primary substrate having pile fibers looped through it, an adhesive and scrim constitutes the double-backed carpet.
Currently, carboxylated styrene-butadiene copolymers are mainly employed as laminating adhesives for rugs and carpets and have to a very great degree replaced natural rubber for such applications. Synthetic latex prepared from carboxylated styrene-butadiene polymers have several important disadvantages. One of the disadvantages of the conventional carboxylic styrene-butadiene latex adhesives is that they have a strong odor of ammonia associated with them. In addition, finished carpets often have a heavy and unpleasant odor of styrene. Carboxylated butadiene-styrene polymer adhesives can also contain some residual unsaturation which tends to cause unsatisfactory aging characteristics and result in a loss of flexibility. In fact, polymerization which occurs as a result of such residual unsaturation has caused the backing of rugs and carpets to become as stiff as a board after only a few years.
The advent of certain synthetic materials in the carpet industry which permit a carpet to be used both indoors and outdoors has given rise to further problems in connection with the preparation of carpeting. Polypropylene is a relatively cheap material which in most respects is quite satisfactory for use as the pile fiber, the primary substrate and the scrim or secondary substrate of a carpet. However, polypropylene presents an adhesion problem since latex compositions normally employed in carpet manufacture do not adhere well to the surface of polypropylene. Carpets prepared using polypropylene and conventional latex compounds have been subject to delamination of the scrim secondary substrate. In order to overcome this problem, it has been suggested that multiple intervening adhesive layers be employed resulting in increased production costs.